User Account Control (UAC) notifies you when programs try to make changes to your computer. Each time you see a UAC dialog box, you need to decide whether or not to allow that program to make changes. Here are some things to consider when making your decision:
Were you expecting to see the message? Were you doing an activity, such as installing software or trying to change Windows settings? If the answer is yes, you can probably expect to see a prompt from UAC. If you aren’t trying to install software or make changes to your computer and you’re prompted unexpectedly, carefully review the prompt. It’s always safest to click No.
Check the name of the program, the publisher information, and the certificate information. Each UAC dialog box provides you with the name of the program and information about the publisher. If the program has a verified publisher, it means that the program has a valid digital signature. A digital signature helps ensure that the program is what it claims to be and comes from a reputable publisher. If the program has a valid certificate, you can also view information about the certificate by clicking Details, and then clicking the certificate link. The certificate information tells you who the certificate was issued to, who the certificate was issued by, and the dates that the certificate is valid.
If the program has an unknown publisher, it doesn't have a valid digital signature from its publisher. This doesn't necessarily mean the program is harmful—many older, legitimate programs lack signatures. However, you should use extra caution and allow a program to run only if you obtained it from a trusted source, such as the original CD or a publisher's website. If you’re unsure, look up the name of the program on the Internet to determine if it’s a known program or malicious software.
Check the file origin. You should be especially careful with programs that are downloaded from the Internet. If you recognize and trust the publisher, it‘s probably safe to run a program that you downloaded from the Internet. If you are unsure about the program or the publisher, you can check the program using a malware scanner or look up the name of the program on the Internet to determine if it is a known program or malicious software.
For more information about UAC, see What is User Account Control?
and What are User Account Control settings?